Microscopic dynamics of granular materials

Dippel, S.

Report

FZJ-2013-04521

Microscopic dynamics of granular materials

Dippel, S. (Corresponding author)FZJ*

1998
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich Jül-3510, 158 pp (1998)

Please use a persistent id in citations: http://hdl.handle.net/2128/4420

Report No.: Juel-3510

Abstract: In the present dissertation, the motion of inelastic spheres on a rough inclined plane is investigated by means of numerical simulations. In a special case, a theoretical model for the motion is pre::>ented i:L::> weH. After an overview of the physics of granular media and abrief outline of existing theoretical models and their limits, the simulation methods used in the present work are explained, where the focus is on time-step driven and event driven moleculaI' dynamics. Advantages and disadvantages are discussed, as well as possible artifacts. In time-step driven moleculaI' dynamics simulations the contact forces acting between particles have to be specified. Since there is no generally accepted force model available for granular materials, a number of common force models is investigated by simulations of simple sampie systems. These simulations are compared with experiments (binary collision of spheres) and ßnalytical results (a cylinder pushed along a plane by a block). It is shown that some force laws - exhibit unphysical behaviour. In some, though not all , of these cases, possibilities to evite these problems by simple physically motivated modifications are presented. The central part of this worle deals with the motion of a sphere on a rough inc1ined plane. By means of moleculaI' dynamics simulations the mechanisms leading to a steady state and its limits are investigated. It turns out that this mechanism leads to independence of the mean steady state velocity of material parameters like the normal restitution coefficient and the coefficient of friction. Based on this observation, a simplified and analytically solvable model for the motion in two dimensions is presented which approximates the steady state velo city and the lower limit of the steady state very weIl. In the 3-dimensional case very similar characteristics of the motion are present, but the 2-dimensional model could not be extended to this case. In the 3-dimensional case, also the fluctuations of the motion are investigated and compared to experimental results. Finally it is checked in how far the results obtained for the single partic1e are valid for the flow of many particles on the inc1ined plane. Here, simulations are restricted to a 2-dimensional system. After a general discussion of previous experimental, numerical and theoretical results on this particular system it is shown for the first time, that for a very broad range of coefficients of restitution the flow profiles of most quantities characterizing the flow do not depend on this coefficient. Particularly the density and velo city profiles are independent of the coefficient of restitution. The coefficient of friction, however, strongly influences the motion, since it strongly increases the dissipation in the system

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